1. Field of the Invention
The present invention relates to a process for producing substantially exclusively beta phase quinacridone.
2. Description of the Prior Art
U.S. Pat. No. 3,257,405 discloses the synthesis of quinacridone by ring closure of 2,5-diarylamino-terephthalic acids with at least 105% orthophosphoric acid (H3PO4) as a dehydrating or ring closing agent. The reaction mixture is cooled, drowned in water or alcohol, and filtered to produce a finely divided pigment. Examples 1 to 13 of this U.S. Patent illustrate the ring closure of 2,5-dianilino-terephthalic acid, while Example 16 illustrates the ring closure of 2,5-panisidino-terephthalic acid. See also U.S. Pat. No. 3,342,823.
U.S. Pat. No. 2,969,366 discloses that quinacridone and its derivatives can be produced in alpha, beta and gamma crystalline forms. However, it teaches that it is difficult to synthesize these compounds exclusively in a single crystalline form.
The beta and gamma forms of quinacridone are more stable than the alpha crystalline phase. Therefore, the prior art has sought methods to synthesize these pigments either entirely in one of the desired crystalline phases, or alternatively, through post-synthesis xe2x80x9cconditioningxe2x80x9d steps to convert crude quinacridone containing a mixture of crystalline phases to a single, desired, phase. For example, U.S. Pat. No. 3,311,630 discloses the production of beta-phase quinacridone by dissolving crude quinacridone in methylsulfonic acid and reprecipitating it by dilution with water. Similarly, U.S. Pat. No. 3,326,918 discloses producing beta-phase quinacridone by dissolving quinacridone in a mixture of an aromatic sulfonic acid and an organic solvent such as toluene, xylene and naphthalene, followed by precipitation into water.
U.S. Pat. No. 3,317,539 discloses the conversion of crude 2,9-dimethoxyquinacridone to the beta-phase by dry milling the crude with sodium chloride and treating with glacial acetic acid, or by milling with sodium chloride in the presence of tetrachloroethylene, xylene or orthodichlorobenzene.
U.S. Pat. No. 3,534,044 discloses the production of beta-phase quinacridone by milling a linear quinacridone of random or unspecified phase in an inorganic salt and formic, acetic, acrylic or substituted acetic acid until the beta-phase crystal modification is obtained.
U.S. Pat. No. 3,940,399 discloses a process for producing gamma-phase quinacridone pigment by heating a mixture of dianilino-terephthalic acid containing 10 to 20 weight (wt. %) percent of di(ortho substituted)anilino-terephthalic acid above 70xc2x0 C. in polyphosphoric acid, and thereafter recovering the gamma quinacridone by adding water to the mixture. The ortho substituents include halogens, alkyl, alkoxy, halogenated alkyl, and tri-halogenated alkyl.
Herbst and Hunger, Industrial Organic Pigments 463 (2nd ed. 1997) teaches that under certain conditions, unsubstituted quinacridones and various substituted quinacridones mix with each other within the crystalline lattice to form solid solutions. These solid solution are different from both the physical admixture of such compounds and from the individual compounds themselves, often giving unexpected and unpredictable tinctorial results and/or pigmentary properties.
An object of the present invention is to economically produce a substantially pure form of beta-phase quinacridone, having an intense blue shade, by employing a minimum amount of polyphosphoric acid as the synthesis reagent.
It is a feature of this invention that the beta-phase quinacridone is produced by ring closure of 2,5-dianilino-terephthalic acid in the presence of a small amount of 2,5-panisidino-terephthalic acid (e.g. along with the polyphosphoric acid). It is an advantage of this invention that the amount of polyphosphoric acid employed is kept to a minimum and that the beta-quinacridone produced does not require a post-synthesis conditioning step. Relatively large amounts of polyphosphoric acid is disfavored as it must be disposed of after the synthesis.
In one aspect, the present invention is a process for producing beta-phase quinacridone, comprising
(i) reacting 1 part by weight of 2,5-dianilino-terephthalic acid with 2.5 to 7 parts by weight polyphosphoric acid, having an acid content of at least 100% measured as H3PO4, in the presence of 2,5-dianisidino-terephthalic acid at a reaction temperature of at least 85xc2x0 C. thereby producing a quinacridone reaction mixture;
(ii) diluting said reaction mixture with 0.05 to 1.0 parts by weight water, thereby producing a diluted mixture;
(iii) drowning said diluted mixture in a water-miscible C1-C6 alkanol thereby producing a slurry;
(iv) heating said slurry to a temperature of from about 100 to about 130xc2x0 C. at a pressure of from about 20 to about 50 pounds per square inch (psi); and
(v) recovering said beta-phase quinacridone product.
In another aspect, the present invention relates to a quinacridone composition, wherein the quinacridone pigment is substantially pure in the beta-phase, containing from 1 to 20 wt. % 2,5-dianisidino-terephthalic acid, based on total weight of the composition, exhibiting an absorption band at 1213 cmxe2x88x921 (analyzed by dispersive infrared spectroscopy).